Recording and reproducing sound



April 20, 1937. v M BENDER 2,077,388

RECORDING AND REPRODUCING SOUND Original Filed May 21, 1931 2 Sheets-Sheet l INVENTOR 122 H qw r' zx tg w April 20, 1937. M. BENDER 2,077,388

RECORDING AND REPRODUCING SOUND Original Filed May 21, 1951 2 Sheets-Shet' 2 Patented Apr. 20, 1937 RECORDING AND REPRQDUCING SOUND Max Bender, Astoria, N. Y., assignor, by mesne assignments,'to United Acoustigraph Corporation, a corporation of Nevada Application May 21, 1931, Serial No. 539,103

. Renewed January 14, 1936 13 Claims.

This invention relates to recordingand reproducing of sound and one object of the invention is to provide an improved method and apparatus for recording sound in the form of a hill and dale groove on a relatively hard flexible material such as a film of celluloid or the like.

A further object of my invention is to provide an improved apparatus for reproducing sound from a groove record.

A further object of my invention is to provide an improved apparatus for cutting a helical or spiral groove ona continuous sheet of flexible material.

A further object of my invention is to provide an improved cutting and an improved recording stylus and an improved method and apparatus for recording and reproducing wherein the styluses employed are of such form and so positioned with respect to the film as to permit recording over substantially the entire range of audible frequencies and reproduction from the record without substantial distortion or appreciable surface sound. A further object of my invention is to provide an improved method and apparatus of the character described, by means of which the film is moved or manipulated in the recording operation so as to produce an accurate sound record as will be more particularly pointed out hereafter.

Other objects of my invention will appear from the following description taken in connection with the accompanying drawings wherein Figure l'is a side elevation partlyin section of an improved combined electromagnetic recorder and reproducer together with its support and an improved recording and reproducing are or anvil over which the film is drawn during recording and reproducing operations;

Figure 2 is a sectional view taken on the line 2-2 of Figure 1;

Figure 3 is a horizontal line3-3 of Figure 1;

Figure 4 is an enlarged detail view showing one form of cutting stylus in contact with the moving sectional view'on the lus adapted to operate in a hill and dale record groove; and

Figures 12 and 13 are similar respectively to Figures 10 and 11 by showing a slightly modified form of pickup stylus.

Referring to Figures 1 and 2 of the drawing 10, represents an electromagnetic device which is d6..- signed to function as an electromagnetic recorder and reproducer. The device Ill hasa cutting or impressing stylus -I l for forming a hill and dale sound record groove on a film l2 as the film is drawn over an are or anvil IS. The film l2 may be formed of plasticized cellulose material or similar material such as employed for photo graphic films. The device It is also provided with a reproducing stylus l4 for reproducing sound from the record groove formed by the stylus ll, suitable means being provided for moving the device Ill toward the right as shown in Figure 1 so as to cause the reproducing stylus to engage in the sound groove as will be; more fully explained hereafter.

The device l0 comprises an electromagnet 20 which is adapted to be supplied with constant current for reproducing a permanent magnet field. Secured to the magnet 20 are frame pieces 22 of magnetic material to which are secured four pole pieces 24. These pole pieces are screwthreaded through the frame pieces so as to be adjustable vertically. Mounted on each of the pole pieces 24 is a winding 26 adapted to be connected in the outputcircuit of an amplifier or other system controlled in accordance with the signal vibrations to be recorded, the circuit connections to the coils 26 being such that the varying currents tend to make adjacent upper poles of opposite polarity and opposed upper and lower poles of opposite polarity.

Mounted to rock in the space between the pole pieces 24 is an armature 21 of soft iron which is pivotally mounted at its center in pivot bearings 29 and 30 mounted respectively in an inner frame piece 32 and an outer frame piece 33 both formed of nonmagnetic material such as brass. The pivot bearing 30 is screwthreaded through the frame piece 33 and is adjustable as shown. Adjustably secured to the armature 21 at one side' of the center of the armature is a rod 38 of nonmagnetic material such as phosphor bronze. Rod 38 is preferably secured to the armature by a universal joint and is pivotally secured on its lower end 56 to a lever 60 of light material such as aluminum and which is snugly pivotally secured at 59 to a downwardly extending rigid bracket 62 formed of nonmagnetic material. All of the above described joints or bearings should be tight. The opposite end 64 of the lever 60 is flattened transversely and is designed to move between upper and lower cushion or damping devices 66 and 61 respectively.

The cutting tool 65 which carries the cutting or impressing jewel or stylus I I is rigidly secured to lever 60 at a point adjacent the pivotal connection 56, suitable means being provided for clamping the tool to the lever and if desired changing the angulation of the needle with respect to the film. The cutting tool 65 comprises a shank 86 of metal such as brass in one end which is secured or imbedded the stylus II formed of hard material such as sapphire, carborundum or diamond or other material having a hardness over 8. The particular form or shape of the stylus or jewel as well as its angulation with respect to the film is an important feature of the present invention and will be described in detail hereafter.

The reproducing stylus I4 is preferably a jewel secured or imbedded in the end of a shank 81 adjustably secured to the lever 60 preferably at a point nearer the fulcrum 59 of the lever than the stylus II. By mounting the recording and reproducing styluses in the relative positions shown the lever 60 and armature 21 are vibrated with greater amplitude in reproducing than in recording, which in many cases is a desirable condition. While I have shown the stylus I4 as pointing vertically downward, in certain cases it is advisable to mount it so that it points substantially in the same direction as the cutting stylus I I so that when the device I is shifted for reproducing, the stylus I4 will engage the film at substantially the same angle as that of the cuttin stylus.

The device III, in the form of invention illustrated, is carried by an arm. 88 pivoted on a horizontal pin or shaft 89 and adjustably counterbalanced at 90 so as to relieve the film of a portion of the weight of the device. Ill and connected parts. For positioning the device It in proper relation to the film so that it will ride on the film as the film is moved over the anvil I 3;, I have provideda downwardly extending adjustable rod 9| screwthreaded into the lower frame piece 22 and adapted to be held in such position by a lock nut 92. The lower end of the rod SI carries a smooth jewel 93 which rides on the upper surface of the film.

At 95 I shOW a convenient means for shifting the device Ill longitudinally of the supporting arm 88 when it is desired to change from recording to reproducing, it of course, being understood that the film I2 is moved toward the left in Figure 1 in both recording and reproducing operations. It will also be understood that in reproducing the stylus I4 is positioned on substantially the point of the anvil at which the recording stylus was positioned in the cutting operation. The means for shifting the device It comprises a bolt 96 extending through a slot 91 in the lower frame piece 22 and screwthreaded into the arm 88 by loosening the bolt 96 the device III may be shifted, along the arm, this arm being provided with guiding ribs 98 to provide lateral movement of the device III.

One important feature of the present invention is the condition or the form or manner of movement of the film material as it is being cut by the recording stylus. The anvil I3 which is preferably formed of metal such as steel has a. smooth upper guiding surface for the film. The fili'n is fed against the cutting edge of the stylus I I under considerable tension and it will be noticed from Figure 1 that the film I2 as it passes the stylus is moving over an arc IIIII of relatively short radius. In practice I find that for films of two to five mils in thickness an arc radius of a quarter of an inch is very satisfactory although considerable variation from this exact radius is permissible. It is generally preferable to form a relatively light out which does not penetrate very far into the body of the film. Inasmuch the upper surface of the film in passing over the arc I09 is stretched, the radius of this arc should not, in general, be so short as to cause the material of the film to be distorted beyond its elastic limit thus tending to cause a more or less permanent bend in the film. It is clear that a thin film an be bent without objectionable distortion over anarc of shorter radius than a thick film and consequently the lower limits of the permissible radius of the arc are different for films of different thicknesses. I find that employing an arc of relatively short radius results in greatly improved recording over that obtainable under the same conditions but with an arc of long radius.

The anvil shown in Figure 1 has an approaching actuate guiding surface 91' and a guiding surface 98 over which the film passes after cutting, the latter surface being shown ap'proxi mately flat.

The anvil I3 shown in Figure 8 is in the form of a rib having a cutting arc of short radius at its apex with guiding faces at opposite sides which are symmetrically arranged with respect to its vertical axial plane. The anvil I3 shown in Figure 9 is in the form of a cylinder or rod of uniform radius.

Another feature of the present invention is the form of the recording stylus and its angulation with respect to the film. In Figure 4 I show on an enlarged scale one form of stylus in contact with the moving film. This stylus has a lower conical side I02 and an upper side I03 which meets the lower side in a curved cutting edge I04. As shown in Figure 4 the angle 0 between the sides IIIZ and I03, that is, the angle between the line formed by the intersection of a vertical plane with side I02 and the line formed by the intersection of such plane with the side I03 is substantially 55. The above mentioned vertical plane as may be seen from a comparison of Figures 4 and is a plane normal to and coincident with the longitudinal central axis of the face. I03. The angle A between the upper side I03 and the normal to the film as it passes the cutting point is 20. "This leaves 15 as the clearance angle B between the lower side or surface I02 and the tangent to the film at the cutting point. I find that the angle A as well as the clearance angle B between the lower side I02 and a tangent to the film are very important in securing a proper cutting. The angle A should be between 17 and 25". This would leave, with the angle 0 55, a clearance angle B of to 18. It is important that there be a substantial clearance angle preferably at least 10". I findthat these angles can be preserved and at the same time the jewel made of suflicient strength and rigidity to hold up under the severe strains and wear to which it is subjected in the cutting operation. The stylus shown in Figures 4- and 5 may be formed from a cylindrical blank by tapering one side to form a curved inclined surface I06 and then cutting off the tapered end so as to form the cutting side I03 which may be substantiallyfiat thus forming a circular or curved cutting edge I04 where the face I03 joins the side I02. The

obtuse angle formed by the sides I03 and I06 adds considerably to the strength of the jewel.

In Figures 6 and 7 I show a modified form of stylus of cylindrical shape with an inclined end which is hollowed out to form an upper cutting surface H0. The angle between the plane of the outer edge of the surface H and the lower face II I of the cylinder that is between this plane and each element of the cylinder may be as great.

same. In the use of the stylus shown inFigures 6 and '7 the angle between the cutting surface I I0 and the normal to the film is maintained between 17 to 25 preferably 20 as in Figure 4. It will thus be seen that there is a relatively large clearance angle between the lower face of the stylus and the film.

The groove cut by the styluses shown in Figures 4 and 6 will be elliptical or approximately cylindrical in section- With variations in depth and corresponding variations in width to form the sound record. In Figures 10 and 11 I show enlarged front and side elevations of a pickup stylus I I3 which is designed to contact with the bottom of the sound groove throughout all or a substantial portion of the width of the groove and at the same time is adapted to follow accurately the undulations of the groove. The stylus II3 which is preferably althoughnot necessarily formed of sapphire has opposite flattened downwardly tapering surfaces II! which curve toward one another at their lower ends as shown in 'I I6 and form a rounded end or edge 6', curved longitudinally to fit the cross sectional contours of the sound groove. The transverse curvature of the lower end at II should not be greater than the curvature of the trough of the undulations of "the record at the highestfrequency to be recorded. To provide for substantially complete contact of the pickup stylus withthe bottom of the groove throughout the width of the groove the pickup stylus should be inclinedto the film at substantially'the same angle as the cutting edge ofthe. recording stylus. The curve H6 as well as the curve I I6 should in general be elliptical although considerable departure from this form is permissible.

In Figures 12 and 13 I show a modified form of reproducing stylus which comprises a jewel or steel point I20 having flat sides I2I which meet in a rounded lower end forming a rounded edge for engagement with the film. Jewel I20 is set in a shank I22 of brass or similar material.

By the use of the invention herein described 'I have been able to record on a film moving at the rate of 60 feet a minute, sound vibrations throughout the audible range up to a frequency in excess of 5,000 and to reproduce without appreciable distortion and without perceptible surface sound and by recording and reproducing at a film speed of 90 feet a minute I am able materially to increase the upper frequency range.

Having described my invention, what I claim and desire by Letters Patent is:

1. The method of cutting a hill and dale sound recor'dgroove in a thin flexible film of tough plasticized material by means of a cutting tool formed with a sharp cutting edge which, method consists in causing said tool-to vibrate in directions substantially normal to the film in accordance with sound waves to be recorded and drawing film'against said edge over an are which, at the point of cutting, has radius substantially less than one half inch.

2. The method of cutting .a hill and dale sound record groove in. a thin flexible film of tough plasticized material by means of a cutting tool .formedwith a sharp cutting edge, which method consists incausing said tool to vibrate in directions substantially" normal to the film in accordance with sound wavesto be recordedand drawing film under relatively great longitudinal tension against said edge over an are which, at the point of cutting, has radius substantially less than one half inch.

3. The method of cutting a hill and dale sound record groove ina thin flexible film of tough plasticized material by means of a cutting. tool formed with a sharp cutting edge which, method consists in causing said tool to vibrate in directions substantially normal to the film in accordance with sound waves to be recorded and drawing film against said edge over an are which, at the point of cutting, has radius substantially less than one half inch and greater than that sufficient to cause a permanent bend in the film.

4. The method of cutting a ,hill and dale sound record groove in. a thin flexible filmof tough plasticized material by means of a cutting tool formed with 'a sharp cutting edge which,

method consists in causing said tool to vibrate in cordance with sound waves to be recorded and drawing film under relatively great longitudinal by means of a tool formed with two surfaces meeting at an angle of from to 60 to form a cutting edge, which method consists in drawing said film against said edge, said film being sharply bent at said edge and vibrating the tool in a direction substantially normal to said filmfwhile supporting said tool with one of said faces adjacent said film-and the other of said faces at an angle of from 17 to 25 from the normal to said film measured in a direction of movement of the film.

'6. The method of cutting a hill and dale sound record groove in tough plasticized material by means of a tool formed with two surfaces meetingiat an angle of less than to form a cutting edge, which method consists in drawing said film against said edge, said film being sharply bent at said edge and vibrating the tool in direction substantially normal to said film while supporting said tool with one of said faces adjacent said film at an angle substantially in excess of 7 thereto andthe other of said'faces at an angle of more than 17 from the normal to said film measured in a direction of movement of the film.

'7. The method of cutting a .hill and dale sound record groove in tough plasticized material by means of a tool formed with two surfaces meeting at an angle of from 45 to 60 to form a cutting edge, which method consists in drawing said film against said edge over an arc of substantially less one inch diameter, and vibrating thetool in a direction substantially normal to said film while supporting said tool with one of said faces adjacent said film and the other of said faces at an angle of from 17 to 25 from the normal to said film measured in a direction of moveagainst said edge over an arc of substantially less a film of tough material comprising a solid cylindrical shank tapered toward one end of the stylus and a cutting face at the end, meeting said taper at one side in a projecting obtuse angle and meeting the taper at the other side of said stylus at an angle of substantially to form a curved cutting edge. 0

10. A small stylus for cutting a sound groove in a film of tough material, comprising an elongated shank of curved section tapered toward. one end of the stylus and a cutting face at the end meeting said taper at one side of the stylus in a projecting obtuse angle and meeting the taper at the other side to form a curved cutting edge, the

angle of the said cutting edge being at no point material and the other of said first named sur-' faces at an angle of more than 17 to the normal to the surface of said material measured in a direction of movement and means for vibrating said tool in directions normal to said surface in accordance with sound vibrations to be recorded. 12. The method of cutting a hill and dale sound record in a flexible film, which consists in feeding the film and bending it just below its elastic limit at a point, and cutting a sound record therein at said point by means of a sharp cutting stylus held against the motion of the film.

13:. The method of cutting a hill and dale record groove'in a film having the properties of tough plasticized material by means of a tool having a curved cutting edge, which method consists in drawing said film against said edge while sharply bending said tool against said edge and vibrating the tool in a direction substantially normal to the film. MAX BENDER. 

